Andrew Silberman is an American Friend living in Tokyo. He received this text written by a field engineer specialized in nuclear reactors who worked at the Fukushima plant. He shares some rationale about what is really happening there and why the situation is not as bad as the English-speaking media are broadcasting.
Good morning/ afternoon/ evening. I sincerely hope that you and you family are coping well with this unprecedented disaster. At this point it appears from the local news that any future tsunami threats have been downgraded or eliminated at this time. Now what is on my mind and perhaps yours is the situation at the nuclear power plants. I would like to share with you that I spent the first 7 years of my career working in the nuclear industry.
I was a field engineer who spent many hours on top of, along side of, and underneath the actual reactor pressure vessel. In the late 1990s I project managed the fabrication of replacement parts that are currently inside of Fukushima 3 and 5. So I would like to share my opinion in the hopes that it may alleviate some of your concerns.
What has happened at Fukushima site is of course not a good thing. But I get concerned with how the media, particularly the English-speaking networks, are portraying things. For example, words like “meltdown” should not be used so casually.
Lets start with the overall construction of the reactor (see attached). The fuel is placed inside a heavy wall steel vessel called the pressure vessel. Surrounding the pressure vessel in very thick concrete. This is called the primary containment. Then surrounding this is more concrete which is called the secondary containment. Covering all of this is the reactor building which is steel. This reactor building on Fukushima 1 is what we have seen on TV blow up the other day. Again, not a good thing but there are still potentially two layers of concrete and one thick layer of steel protecting the fuel.
From what I have gathered from a few different sources, some of the fuel may have melted inside the pressure vessel but the vessel has not been compromised.
There have been reports from TEPCO of increased radiation exposure at the plant boundary. The largest spike that I heard about was two days ago at a level of 500 microSievert/ hour. A microSievert if a measurement of a dose of radiation. So at 500 microSievert/ hour, if you stood at the boundary for 1 hour you would receive a total dose measuring 500 microSieverts. Now the intensity of radiation dissipates rapidly as you get further away form the source. Imagine standing in the center of a dark room next to a single light bulb. As you walk further away from the light it would get more and more difficult to see by it. If we assume that the plant boundary is at 1 km from the source, then at 20 km the level would be at 1.25 microSievert/ hour. In Tokyo approximately 200 km away, the level would have been .0125 microSievert/ hour. So even if you were standing at the 20 km exclusion zone boundary for an entire month and the spiked level maintained the entire time, the total dose received would still be lower than the Japanese government allowable rate of 1000 microSievert/ year.
As far as radiation exposure, I wanted to let you know we all receive radiation in very small doses in our everyday lives. For example, if you take a 10 hour flight; say Tokyo to Auckland, Chicago, or Munich, you will receive approximately 50 microSieverts of radiation.
I hope this helps you sleep a little better during these trying times.